package/liquid-dsp: add missing dependency on fftw

When one of BR2_PACKAGE_FFTW_PRECISION_* is enabled, liquid-dsp links
against fftw3f, fftw3 or fftw3l, but forgets to add the fftw package
in its dependencies. It works fine in practice because "fftw" is
before "liquid-dsp" in the alphabetic ordering, but building with
"make liquid-dsp" or with per-package directory causes a build
failure.

Fix that by adding the missing dependencies.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Tested-by: Gwenhael Goavec-Merou <gwenhael.goavec-merou@trabucayre.com>
Reviewed-by: Gwenhael Goavec-Merou <gwenhael.goavec-merou@trabucayre.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit 2517fa73edcb48d05fae7795ea75591e004a0177)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/liquid-dsp/liquid-dsp.mk

@@ -32,6 +32,7 @@ endif
 # use FFTW instead of built-in FFT
 ifeq ($(BR2_PACKAGE_FFTW_PRECISION_SINGLE),y)
 LIQUID_DSP_LDFLAGS += -lfftw3f
+LIQUID_DSP_DEPENDENCIES += fftw
 endif
 
 # disable altivec, it has build issues
@@ -41,10 +42,12 @@ endif
 
 ifeq ($(BR2_PACKAGE_FFTW_PRECISION_DOUBLE),y)
 LIQUID_DSP_LDFLAGS += -lfftw3
+LIQUID_DSP_DEPENDENCIES += fftw
 endif
 
 ifeq ($(BR2_PACKAGE_FFTW_PRECISION_LONG_DOUBLE),y)
 LIQUID_DSP_LDFLAGS += -lfftw3l
+LIQUID_DSP_DEPENDENCIES += fftw
 endif
 
 LIQUID_DSP_CONF_OPTS += \