selftests/intel_pstate: fix operand expected error

Running "make kselftest TARGETS=intel_pstate" results in
the following errors:
- ./run.sh: line 90: / 1000: syntax error: operand expected
(error token is "/ 1000")
- ./run.sh: line 92: / 1000: syntax error: operand expected
(error token is "/ 1000")

This fix allows to have cross-platform compatibility when
using arithmetic expression with command substitutions.

Link: https://lore.kernel.org/r/f37df23888cd5ea6b3976f19d3e25796129dd090.1730141362.git.alessandro.zanni87@gmail.com
Signed-off-by: Alessandro Zanni <alessandro.zanni87@gmail.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

Author: Alez87

tools/testing/selftests/intel_pstate/run.sh

@@ -87,9 +87,9 @@ mkt_freq=${_mkt_freq}0
 
 # Get the ranges from cpupower
 _min_freq=$(cpupower frequency-info -l | tail -1 | awk ' { print $1 } ')
-min_freq=$(($_min_freq / 1000))
+min_freq=$((_min_freq / 1000))
 _max_freq=$(cpupower frequency-info -l | tail -1 | awk ' { print $2 } ')
-max_freq=$(($_max_freq / 1000))
+max_freq=$((_max_freq / 1000))
 
 
 [ $EVALUATE_ONLY -eq 0 ] && for freq in `seq $max_freq -100 $min_freq`