Fix CFLAGS parameter

Fix CFLAGS parameter

Currently nvme-cli 1.7 is not compiling on Debian because the Debian helper
(compilation toolkit) does pass a CFLAGS variable, thus, avoiding the
initial definition (CFLAGS ?= -O2 -g -Wall -Werror -I.)

The problem is that -I should not be removed, otherwise the code does not
compile, with the following bug:

	cc -Wdate-time -D_FORTIFY_SOURCE=2 -D_GNU_SOURCE -D__CHECK_ENDIAN__ -g -O2 -fdebug-prefix-map=/home/breno/nvme/nvme-cli-1.7=. -fstack-protector-strong -Wformat -Werror=format-security -std=gnu99 -DLIBUUID -DNVME_VERSION='"1.7"' -o plugins/intel/intel-nvme.o -c plugins/intel/intel-nvme.c
	plugins/intel/intel-nvme.c:10:18: fatal error: nvme.h: No such file or directory
	compilation terminated.

This patch just moves the -I parameter to part of the CFLAGS that is not
replaced by dh's CFLAGS.

Signed-off-by: Breno Leitao <leitao@debian.org>