Fix Linux FMV bank verification

[MysteriousAeon]

Fixes #8.

tools/build-linux.sh enables pipefail and previously checked for the FMV runtime bank with:

strings "$BIN" | grep -q mph_arm9_fmv_runtime

When grep -q finds a match, it exits early and strings can receive SIGPIPE. With pipefail enabled, that makes the pipeline return 141 even though the runtime bank is present.

This replaces the pipeline with a direct binary search:

grep -a -q mph_arm9_fmv_runtime "$BIN"

Verified locally:

old check: 141
new check: 0
bash -n: 0
git diff --check: 0

The change is limited to one line in tools/build-linux.sh.