MIPS: pgtable: fix -Wshadow in asm/pgtable.h

Solves the following repetitive warning when building with -Wshadow:

In file included from ./include/linux/pgtable.h:6,
                 from ./include/linux/mm.h:33,
                 from ./include/linux/dax.h:6,
                 from ./include/linux/mempolicy.h:11,
                 from kernel/fork.c:34:
./arch/mips/include/asm/mmu_context.h: In function ‘switch_mm’:
./arch/mips/include/asm/pgtable.h:97:16: warning: declaration of ‘flags’ shadows a previous local [-Wshadow]
   97 |  unsigned long flags;      \
      |                ^~~~~
./arch/mips/include/asm/mmu_context.h:162:2: note: in expansion of macro ‘htw_stop’
  162 |  htw_stop();
      |  ^~~~~~~~
In file included from kernel/fork.c:102:
./arch/mips/include/asm/mmu_context.h:159:16: note: shadowed declaration is here
  159 |  unsigned long flags;
      |                ^~~~~
Signed-off-by: NAlexander Lobakin <alobakin@pm.me>
Signed-off-by: NThomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/include/asm/pgtable.h

@@ -94,31 +94,31 @@ extern void paging_init(void);
 
 #define htw_stop()							\
 do {									\
-	unsigned long flags;						\
+	unsigned long __flags;						\
 									\
 	if (cpu_has_htw) {						\
-		local_irq_save(flags);					\
+		local_irq_save(__flags);				\
 		if(!raw_current_cpu_data.htw_seq++) {			\
 			write_c0_pwctl(read_c0_pwctl() &		\
 				       ~(1 << MIPS_PWCTL_PWEN_SHIFT));	\
 			back_to_back_c0_hazard();			\
 		}							\
-		local_irq_restore(flags);				\
+		local_irq_restore(__flags);				\
 	}								\
 } while(0)
 
 #define htw_start()							\
 do {									\
-	unsigned long flags;						\
+	unsigned long __flags;						\
 									\
 	if (cpu_has_htw) {						\
-		local_irq_save(flags);					\
+		local_irq_save(__flags);				\
 		if (!--raw_current_cpu_data.htw_seq) {			\
 			write_c0_pwctl(read_c0_pwctl() |		\
 				       (1 << MIPS_PWCTL_PWEN_SHIFT));	\
 			back_to_back_c0_hazard();			\
 		}							\
-		local_irq_restore(flags);				\
+		local_irq_restore(__flags);				\
 	}								\
 } while(0)