package/openblas: fix build failure due to forced FFLAGS

package/openblas: fix build failure due to forced FFLAGS

Buildroot specifies a value for FFLAGS on the make command-line.
While the openblas makefiles allowed this principle for the most part by
using 'override FFLAGS += ....', the make.inc file generated for the shipped
'lapack' sources just used a 'FFLAGS = ...' statement, whose value is then
eclipsed by the command-line FFLAGS.

This meant that -fPIC may be passed to the link step but not to all relevant
source files, causing relocation failures.

Fixes: http://autobuild.buildroot.net/results/d530db0f37e1e0462e3af1e1787e15f94ff21884/
Signed-off-by: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>