libqmi: move canonicalize_file_name()

libqmi: move canonicalize_file_name()

Previously was defined in qmi-util.h to fix musl
compatibility.  It was missed that this is a shared
header which causes other dependent package builds
to fail, so the static definition was moved into the
implementation where it was used.

Upstream bug report has been updated and this resolves
the following autobuilder related failures.

 http://autobuild.buildroot.net/results/fe9b6b1b1399a4e8aafc6a326c81ec97c2480025
 http://autobuild.buildroot.net/results/40eef797b4d8d53fc6e10f2048316d63549caf6d

test-pkg testing was performed against 10 random toolchains

++ Config snippet ++
BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_EUDEV=y
BR2_PACKAGE_MODEM_MANAGER_LIBQMI=y
BR2_PACKAGE_MODEM_MANAGER=y
BR2_PACKAGE_LIBQMI=y

++ Tested Toolchains ++ (Verified I hit all libc variants)
br-arm-cortex-a9-musl
br-arm-full-static
br-m68k-68040-full    (uclibc)
br-mips32r6-el-hf-glibc
br-mips64-n64-full
br-mips64r6-el-hf-glibc
br-mipsel-o32-full
br-sparc64-glibc
linaro-arm
sourcery-arm

Signed-off-by: Matthew Weber <matthew.weber@rockwellcollins.com>
Tested-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>