mem_tg: fix support for more than 8 memory channels

The sizeof() operator returns the size of an object or type in bytes,
not bits. Instead of calculating the number of bits using, e.g.,
CHAR_BIT * sizeof(), hard-code 64 since it is close to the declaration.

This is a prerequisite for HBM support with up to 32 channels.

Link: #3137
Fixes: 7bf96dc ("mem_tg test multichannel")
Signed-off-by: Peter Colberg <peter.colberg@intel.com>

samples/mem_tg/tg_test.h

@@ -244,8 +244,8 @@ class tg_test : public test_command
       int num_channels = 0;
       if ((tg_exe_->mem_ch_[0]).find("all") == 0) {	
         uint64_t mem_capability = tg_exe_->read64(MEM_TG_CTRL);
-        channels = new int[sizeof(uint64_t)]; // size should be same as mem_capability 
-        for (uint32_t i = 0; i < sizeof(uint64_t); i++) { // number of iterations should be same as mem_capability 
+        channels = new int[64]; // size should be same as mem_capability
+        for (uint32_t i = 0; i < 64; i++) { // number of iterations should be same as mem_capability
           if ((mem_capability & (1ULL << i)) != 0) {
             channels[num_channels] = i;
             num_channels += 1;