test: fix 'diff --unified' failing on Alpine Linux

The long '--unified' flag of the 'diff' command is GNU specific.
Although it is recognized by the Alpine Linux version of 'diff', it is
expecting a numeric argument N (number of lines).

This difference caused test cases using 'diff' to fail on Alpine.

This patch changes that to '-u' which implies N=3 by default on both
GNU-based distros and Alpine Linux.

Signed-off-by: Michal Rábek <[email protected]>

Author: MichaelRabek

libnvme/test/nbft/nbft-dump-diff.sh.in

@@ -5,4 +5,4 @@ if [ $# -ne 2 ]; then
   exit 255
 fi
 
-"@NBFT_DUMP_PATH@" "$1" | diff --unified "$2" -
+"@NBFT_DUMP_PATH@" "$1" | diff -u "$2" -