x86: use kernel_stack_pointer() in kgdb.c

The way to obtain a kernel-mode stack pointer from a struct
pt_regs in 32-bit mode is "subtle": the stack doesn't actually
contain the stack pointer, but rather the location where it would
have been marks the actual previous stack frame.  For clarity, use
kernel_stack_pointer() instead of coding this weirdness
explicitly.
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>
Cc: Jason Wessel <jason.wessel@windriver.com>

arch/x86/kernel/kgdb.c

@@ -88,7 +88,6 @@ void pt_regs_to_gdb_regs(unsigned long *gdb_regs, struct pt_regs *regs)
 	gdb_regs[GDB_SS]	= __KERNEL_DS;
 	gdb_regs[GDB_FS]	= 0xFFFF;
 	gdb_regs[GDB_GS]	= 0xFFFF;
-	gdb_regs[GDB_SP]	= (int)&regs->sp;
 #else
 	gdb_regs[GDB_R8]	= regs->r8;
 	gdb_regs[GDB_R9]	= regs->r9;
@@ -101,8 +100,8 @@ void pt_regs_to_gdb_regs(unsigned long *gdb_regs, struct pt_regs *regs)
 	gdb_regs32[GDB_PS]	= regs->flags;
 	gdb_regs32[GDB_CS]	= regs->cs;
 	gdb_regs32[GDB_SS]	= regs->ss;
-	gdb_regs[GDB_SP]	= regs->sp;
 #endif
+	gdb_regs[GDB_SP]	= kernel_stack_pointer(regs);
 }
 
 /**