powerpc/reg: Remove #ifdef around mtspr macro

That ifdef was introduced by commit 1458dd95 ("powerpc/8xx:
Handle CPU6 ERRATA directly in mtspr() macro") and left over by
commit 2a45addd ("powerpc/8xx: Remove CPU6 ERRATA Workaround")

Remove it.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/cf652e47ea9e453e89813611b6f76d0939a12063.1687344017.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/reg.h

@@ -1414,11 +1414,9 @@ static inline void mtmsr_isync(unsigned long val)
 #define mfspr(rn)	({unsigned long rval; \
 			asm volatile("mfspr %0," __stringify(rn) \
 				: "=r" (rval)); rval;})
-#ifndef mtspr
 #define mtspr(rn, v)	asm volatile("mtspr " __stringify(rn) ",%0" : \
 				     : "r" ((unsigned long)(v)) \
 				     : "memory")
-#endif
 #define wrtspr(rn)	asm volatile("mtspr " __stringify(rn) ",2" : : : "memory")
 
 static inline void wrtee(unsigned long val)