ARM: 8397/1: fix vdsomunge not to depend on glibc specific error.h

If the host toolchain is not glibc based then the arm kernel build
fails with

 arch/arm/vdso/vdsomunge.c:53:19: fatal error: error.h: No such file or directory

error.h is a glibc only header (ie not available in musl, newlib and
bsd libcs).  Changed the error reporting to standard conforming code
to avoid depending on specific C implementations.

Signed-off-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Fixes: 8512287a ("ARM: 8330/1: add VDSO user-space code")
Cc: stable@vger.kernel.org
Signed-off-by: Nathan Lynch <nathan_lynch@mentor.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>