Use HIP_PATH if set else use relative ../...

[ROCm/hip commit: 40e72dcd4a]

projects/hip/samples/0_Intro/bit_extract/Makefile

@@ -1,6 +1,6 @@
 #Dependencies : [MYHIP]/bin must be in user's path.
 
-HIP_PATH=../../..
+HIP_PATH=?../../..
 HIP_PLATFORM=$(shell $(HIP_PATH)/bin/hipconfig --platform)
 HIPCC=$(HIP_PATH)/bin/hipcc
 

projects/hip/samples/0_Intro/square/Makefile

@@ -1,4 +1,4 @@
-HIP_PATH=../../..
+HIP_PATH?=../../..
 HIPCC=$(HIP_PATH)/bin/hipcc
 
 all: square.hip.out