Correct the pkgconfig generated file naming

The typical convention is to not use the `lib` prefix (ie `libfoo`)
but instead to just use foo.

Change-Id: I5ab46418e2a1708d5c11970f1e56250f2adb7d70
Signed-off-by: Mario Limonciello <mario.limonciello@dell.com>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/36069


Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Richard Hughes <richard@hughsie.com>
Reviewed-by: David Hendricks <david.hendricks@gmail.com>