efi/pstore: Return error code (if any) from efi_pstore_write()

efi/pstore: Return error code (if any) from efi_pstore_write()

For some reason return value from actual variable setting was ignored.
With this change error code get transferred upwards through call stack.

Signed-off-by: Evgeny Kalugin <evgeny.kalugin@intel.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20170404160245.27812-9-ard.biesheuvel@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>