util/nvmutil pread: rw_over_nrw exit, not set

otherwise, if it's -1 and errno happens to be
EINTR or EAGAIN, we might loop on what is a
real error. this bug fixes that edge case.

Signed-off-by: Leah Rowe <leah@libreboot.org>

util/nvmutil/nvmutil.c

@@ -2126,7 +2126,8 @@ real_pread_pwrite:
 			else if (rw_type == IO_PWRITE)
 				r = write(fd, mem, nrw);
 
-			r = rw_over_nrw(r, nrw);
+			if (rw_over_nrw(r, nrw) == -1)
+				return -1;
 
 		} while (r == -1 &&
 		    (errno == try_err(loop_eintr, EINTR)