riscv/vdso: typo therefor

The adverbs 'therefor' and 'therefore' have different meaning.
As the meaning here is 'consequently' the spelling should be 'therefore'.
Signed-off-by: NHeinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: NConor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20220925004757.9089-1-heinrich.schuchardt@canonical.comSigned-off-by: NPalmer Dabbelt <palmer@rivosinc.com>

arch/riscv/include/asm/vdso.h

@@ -10,7 +10,7 @@
 
 /*
  * All systems with an MMU have a VDSO, but systems without an MMU don't
- * support shared libraries and therefor don't have one.
+ * support shared libraries and therefore don't have one.
  */
 #ifdef CONFIG_MMU