pv: fix ptests

Setting the RDEPENDS with "=" erased the base dependencies
(notably ${PN} itself) from the list, making the tests fail, unless
the dependencies were installed explicitly.

Signed-off-by: Gyorgy Sarvari <skandigraun@gmail.com>

meta-oe/recipes-support/pv/pv_1.6.20.bb

@@ -17,7 +17,7 @@ inherit autotools ptest
 LDEMULATION:mipsarchn32 = "${@bb.utils.contains('TUNE_FEATURES', 'bigendian', 'elf32btsmipn32', 'elf32ltsmipn32', d)}"
 export LDEMULATION
 
-RDEPENDS:${PN}-ptest = "coreutils"
+RDEPENDS:${PN}-ptest += "coreutils"
 
 do_install_ptest() {
     install -d ${D}${PTEST_PATH}/tests