powerpc/syscalls: Simplify do_mmap2()

When shift is nul, operations remain valid so no test needed.

And 'ret' is unnecessary.

And use IS_ALIGNED() to check alignment, that's more clear.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/373ec500f386374bc5735007df3d3869eac47be1.1624618701.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/syscalls.c

@@ -41,20 +41,13 @@ static inline long do_mmap2(unsigned long addr, size_t len,
 			unsigned long prot, unsigned long flags,
 			unsigned long fd, unsigned long off, int shift)
 {
-	long ret = -EINVAL;
-
 	if (!arch_validate_prot(prot, addr))
-		goto out;
+		return -EINVAL;
 
-	if (shift) {
-		if (off & ((1 << shift) - 1))
-			goto out;
-		off >>= shift;
-	}
+	if (!IS_ALIGNED(off, 1 << shift))
+		return -EINVAL;
 
-	ret = ksys_mmap_pgoff(addr, len, prot, flags, fd, off);
-out:
-	return ret;
+	return ksys_mmap_pgoff(addr, len, prot, flags, fd, off >> shift);
 }
 
 SYSCALL_DEFINE6(mmap2, unsigned long, addr, size_t, len,