dummyflasher: Add error check for file read

Print an error message and return if the read from emu_persistent_image
fails.

Change-Id: Icd1a72f9171e547f2081ba4bc53834a17ef7fcab
Signed-off-by: Jacob Garber <jgarber1@ualberta.ca>
Found-by: Coverity CID 1403912
Reviewed-on: https://review.coreboot.org/c/flashrom/+/34845
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: David Hendricks <david.hendricks@gmail.com>
1 file changed